One trick I have learnt whilst being messed about by funny ignition systems is always to make sure you have enough fuel in the tank (obvious really!!!!!). But sometimes you need more than you think you do to get it to flow over the inlet to the fuel bowl.

When I'm in doubt about whether fuel flow ia adequate I give a whiff of "Easy Start". If the spark from either magneto of distributor is good it will always fire up regardless of fuel supply. This way you get a check on the adequacy or otherwise of the spark,and maybe also an indication that there is not enough fuel in the tank.